1. Field of the Invention
This invention relates to a ball slide bearing and a connecting device associated with a mast for hooking a gas turbine engine under an aircraft wing comprising such a bearing.
2. Description of the Related Art
In the aeronautical industry, it is known to use a ball joint for immobilizing two elements, such as a connecting rod and a structural part, in translational movement relative to one another, while allowing a relative movement in rotation of these elements. Such a ball joint is used, for example, in a device for hooking a mast for hooking an aircraft gas turbine engine under a wing element.
On existing aircraft, the engines are suspended below the wing by a complex hooking device that is also called a hooking mast, comprising a rigid structure in the form of a box that consists of the assembly of longitudinal beams and panels connected to one another by several transversal ribs.
These devices are designed in particular for allowing the transmission to the wing of static and dynamic forces produced by the engines, such as weight, thrust, or else different dynamic forces.
In this connection, in the known hooking devices of the prior art, the transmission of these forces between the rigid structure and the wing is ensured by hooking means that consist of three fasteners, one front fastener that consists of two lateral half-fasteners, a rear fastener, as well as an intermediate fastener that is designed to absorb the thrust forces generated by the associated gas turbine engine.
Referring to FIG. 1, such a hooking device 1 of a gas turbine engine 10 for an aircraft according to the prior art is seen. To analyze the forces, an orthonormed reference point (OXYZ)—in which the OX axis represents the direction that is parallel to a longitudinal axis of this gas turbine engine 10, the OY axis represents the direction that is oriented crosswise relative to this gas turbine engine 10 and to the aircraft, and the OZ axis represents the vertical direction upward—is assigned to the gas turbine engine.
The terms “front” and “rear” are to be considered relative to a direction of advance of the aircraft that is shown diagrammatically by an arrow 7.
More specifically, this device comprises a rigid hooking structure 6 and a set of hooking means 1 inserted between the gas turbine engine 10 and a wing element 2. These hooking means 1 consist of a front fastener 3, an intermediate fastener 4 that is described in more detail below, and a rear fastener 5, whereby the intermediate fastener is placed between the front and rear fasteners.
Furthermore, in this FIG. 1, conventional hooking means 12 inserted between the rigid structure 6 and the gas turbine engine 10 are also shown by way of indication. These hooking means 12 are not part of this invention and consequently will not be described in more detail.
Referring to FIG. 1, it can be seen that the intermediate fastener that is designed to absorb the thrust forces, also called “spigot” fastener, comprises a ball joint 8 and a shaft 9, also called “spigot,” housed in the ball joint. The ball joint and the shaft are attached by means of an attachment fitting to elements of boxes of mast and wing.
More specifically, the attachment fitting for attaching the shaft has an essentially flat support surface that is designed to be attached to the surface of the upper longitudinal beam of the box 6 using known mechanical attachment means. This fitting comprises an integrated shaft or a housing in which a shaft is connected, one or the other being oriented essentially parallel to the OZ axis. During the stowage of the mast, this shaft is housed in the ball joint that is installed in a wing element 2.
Now referring more specifically to FIG. 2A, it is possible to see that the ball joint consists of a set of elements accommodated in an opening that is made in another attachment fitting 13 of a type that is similar to the first. This second attachment fitting also has a flat support surface that is designed to be attached to a surface of the wing element using known attachment means. This unit comprises a first inside ring 15 that has a spherical surface arranged inside a second outside ring 16. The surface of the outside ring that is in contact with the inside surface of the opening of the fitting comprises sliding flat surfaces 31. These surfaces work with corresponding inside flat surfaces of the opening to make possible a movement along the longitudinal axis OX of the gas turbine engine. The two rings are kept within the opening by a tightening plate 14 that works with a brake washer 17. The movement of the axis within the inside ring ensures the movement along the OZ axis. Thus, the intermediate fastener 4 is designed so as to absorb the transverse forces directed in the direction OY.
A major problem in such a structural configuration of the ball joint comes from friction between the flat surfaces of the outside ring and the inside surface of the attachment fitting. Actually, the relative movements under load of the surfaces are accompanied by friction that generates phenomena of contact wear and tear and sliding at the level of the contact surfaces between the outside ring and the attachment fitting. In particular, there is a risk of roughness peaks that are present on the surfaces that rub under the action of contact wear and tear that weld together, which can, under high load, lead to complete locking or jamming of the ball joint. These wear and tear phenomena are all the more critical when the friction surfaces are flat due to the effects of free edges.
Furthermore, when such a problem occurs, it is necessary to change the fitting 13 and the outside ring 16. For this purpose, all of the parts that constitute the connection have to be removed. Since the fitting 13 is attached to a panel that is made of composite material, the fact of withdrawing attachment means and attaching a new fitting can make the composite structure fragile, which can lead to severe deterioration of the mechanical properties of the panel. Maintenance for changing damaged parts therefore proves difficult and expensive.